This invention relates to a method and apparatus for determining the proper operation of an end-of-aisle detector system.
Permanent magnets have commonly been embedded in the floor of warehouses that employ either wire or rail guided vehicles in order to indicate various locations, such as the end of an aisle, the beginning of a spur, or some other location where control action of the vehicle is required. In many prior art vehicles, reed switches have been used to indicate whenever the vehicle passes over one of these magnets.
In wire guidance systems, a wire is buried in the floor, and that wire is normally energized with an alternating frequency current. If the signal from the wire is lost for any reason, then action (usually braking) is taken to prevent further unattended movement of the vehicle and thereby protect the vehicle from damage.
Prior to the vehicle acquiring a signal from the buried wire, the sensors may be checked for proper operation by means of a wire permanently placed in proximity to the sensors. A generator causes a test current of the same frequency to be passed through this wire to create a simulated wire guide path signal having essentially the same magnitude as the buried wire. If this test signal is detected, and the sensors coils and associated amplifiers provide the correct output, then this circuit is deemed functional and a software flag is created to indicate that the hardware is installed and working. This sensor circuit may be checked from time to time, under the direction of the guidance controller, to verify that all is working properly. A circuit of this type is described in copending U.S. patent application Ser. No. 446,902, filed Dec. 6, 1989, now U.S. Pat. No. 5,032,994, and assigned to the same assignee as the present invention.
However, since a buried magnet is detected only occasionally, there is no continuous output from the magnet detector on which to rely to indicate continued reliable operation of the detector. Clearly, it would be desirable to have some means to determine whether the detector and its associated circuit continue to be functional.